Many telecommunications devices include backplanes for transmitting digital information between components of the devices. For example, a telecommunications switching system might include a backplane for transmitting digital data representing voice signals between cards associated with incoming and outgoing ports. Typically, such a system would also include a mechanism to allow the system to detect a framing error or other loss of synchronization between cards, which may occur as a result of a total or partial failure of one of the cards. Successful operation of the system in many instances will depend heavily upon the ability of this mechanism to appropriately detect and respond to such a failure to meet often stringent availability, flexibility, and other requirements placed on the system.
As the telecommunications industry continues to dominate the growth of the global economy, meeting availability, flexibility, and other requirements placed on switching and other systems has become increasingly important. High availability is generally considered as exceeding 99.999 percent availability, amounting to less than approximately five minutes of “down time” per year, and generally requires a system to be able to detect and to autonomously handle certain faults, such as failure of a card causing framing errors or other losses of synchronization, without immediate human intervention. Providing high availability is often a de facto if not explicit competitive requirement for many telecommunications manufacturers.
However, previous techniques for detecting and responding to a framing error or other loss of synchronization are often inadequate to meet high availability and other requirements. One such technique involves comparing, at each card and for each frame, reference signals received from each of two signal generators to detect a framing error or other loss of synchronization between the card and one or both of the generators. If a framing error is detected, the system might raise an alarm to indicate the error, but might otherwise provide no indication of the source of the error -- one generator, both generators, or the card itself. Previous techniques also do not allow the system to continue operating, uninterrupted and maintaining the integrity of data the system is handling, despite failure of one of these components, which may result for example in dropped calls and other undesirable consequences. These and other deficiencies of previous techniques become particularly apparent within high availability backplane environments of telecommunications devices.